Compressor



June 5, 1956 E. A. STALKER 2,749,027

I COMPRESSOR Filed Dec. 26, 1947 3 Sheets-Sheet 1 IN VEN TOR.

M d/ AM June 5, 1956 A. STALKER 2,749,027

COMPRESSOR Filed Dec. 26, 194'? 3 Sheets-Sheet 2 /,,l m INVENTOR. 0 1"June 5, 1956 E. A. STALKER 2,749,027

COMPRESSOR Filed Dec. 26, 1947 5 Sheets-Sheet 3 I N VEN TOR.

United States Patent COMPRESSOR Edward A. Stalker, Bay City, Mich.

Application December 26, 1947, Serial No. 794,018

8 Claims. (Cl. 230-122) My invention relates to compressors.

An object of the invention is to provide a compressor which maintainsits pressure and etficiency over a wider range of volume flow perrevolution.

Another object is to provide blades of successively rounder and thickernoses in successive stages downstream to accommodate a wide range ofangles of approach to the blade.

Still another object is to provide proper relations be tween stator androtor blades to reduce the range of angles of approach which a bladerequires.

Another object is to provide a combination of axial flow stages of onetype with an axial flow stage of another type to ameliorate the greatloss in efliciency at oil-design conditions when the compressor has beendesigned for a high compression ratio.

Other objects will appear from the drawings, specification, and claims.

The above objects are accomplished by the means illustrated in theaccompanying drawings in which:

Figure 1 shows a vector diagram for the air approaching a rotor blade;

Figure 2 shows a vector diagram for the air approaching a rotor blade ata fiat angle;

Figure 3 is a chordwise section along the line 3-3 in Fig. 4;

Figure 4 is an axial section through an axial flow compressor accordingto this invention.

Figure 5 is a fragmentary diagrammatic development of some of the stagesof the compressor of Fig. 4 with the blades shown solid although theyare hollow in the machine;

Figure 6 is a section along line 6-6 in Fig. 4;

Figure 7 is a fragmentary development of the last stage of thecompressor to show the vector relations;

Figure 8 is a fragmentary development of the last rotor showing theblades in section as they are in the machine;

Figure 9 is an alternate rotor construction to that of Fig. 8;

Figure 10 is an enlarged fragmentary axial section through a part of thelast rotor and part of the case of the compressor of Fig. 4;

Figure 11 shows an isolated group of blades and a connecting duct, oneblade having an induction slot and the other having a discharge slot;

Figure 12 is a fragmentary axial section through another compressor inwhich the rotor and stator blades have discharge slots and the otherwalls have slots for facilitating the entrance of a supersonic flow intothe passages between blades; and

Figure 13 is a section along line 1313 in Fig. 12.

When a multi-stage axial flow compressor is operating at a mass flow perrevolution less than the optimum or design value with a back pressurethat is relatively low the axial velocity in the downstream stages maybe as much as three times the velocity which would prevail 2,749,027Patented June '5, 1956 at the optimum or design condition. This is sobecause the upstream stages do a certain amount of compressing at offdesign conditions and the lack of back pressure permits the flowcompressed by the upstream stages to stream at greatly increasedvelocity through the later stages. This leads to a great change in thedirection of the fluid approaching a later rotor or stator with respectto the direction for the optimum operating condition, reducing the angleof attack of the blades and their compressing ability.

For instance Figure 1 shows the vector diagram for a conventional axialflow compressor for a downstream stage when the compressor is operatingunder optimum condition, that is at about best efliciency andcorresponding pressure ratio. In this instance the axial velocity foroptimum operation is Cm equal to a fraction of u the peripheralvelocity. Under this condition the direction of the fluid leaving thestator blade 1 and approaching the rotor blade 2 is the vector 4. Now ifthe axial velocity is increased to 3 times Cm the new direction is thevector 6 and the change in the angle of approach is A041 which is equalto about 30. This is a greater range of angles of attack than a bladecan accommodate.

Now consider a case as in Fig. 2 where the leaving velocity vector fromblade 10 is C directed at the positive angle B toward the rotor blade12. The resultant vector is 14. If the axial component of C is increasedfrom Cm as for Fig. 1 to 3Cm' the new resultant velocity vector is 20whose peripheral component is much larger than that of vector 14. Theperipheral component is not magnified as greatly as the axial since thenew triangle of which 269 is the longer side is not symmetrical with re*spect to the triangle 14 c'u. The change in angle of approach to blade12 is now Auz equal to about 7. This is not only within the range ofangles which the blade can accommodate but is also well within the rangeof angles of attack for best etficiency of the blade itself.

It is thus shown that deflecting the air toward the oncoming rotorblades reduces the range of approach angles or angles of attack whichthe blade must accommodate when the compressor is operating at apressure and speed substantially below optimum conditions provided thedeflection through the angle B is accompanied by a rise in velocity.

The angle B for the vector representing the entering vector for a rotor(or stator) is positive when the vector has a peripheral componentdirected toward the concave face of the blade of the succeeding stage.Thus in Fig. 2, B is positive. Also in Fig. 3, B is positive since thevector 32 approaching the stator attacks the concave side of the blade86.

The range of approach angles which can be accommodated by the downstreamstages can also be extended to a considerable extent by making the nosesof the blades successively thicker in successive stages in thedownstream direction. Thus in Fig. 3 the nose 30 is substantiallysemicircular so that the relative flow will be able to flow about thenose without burbling when the approach vectors vary from vector 32 tovector 34 disposed angularly with respect to each other by the angle 6(delta).

To further encourage the flow the nose is provided with the slots 36 and38 (Figs. 3, 4 and 8) through which a flow may be inducted to controlthe boundary layer.

Since the fluid is compressed in successive stages the temperature risesalong the compressor axis. Consequently the velocity of sound in thefluid increases in magnitude so that the velocity of the fluid relativeto the blades can be increased without precipitating a compressibilityshock. In other words the local velocity on the blade surfaces can behigher on the downstream blades without reaching the critical Machnumber of one.

Thickening the nose of the blades makes possible a wider range of angles5 (see Fig. 3) but increases the local velocity on the nose. However bytaking advantage of the rise in temperature from stage to stage, thenoses of the blades of successive stages may be thickened without thelocal Mach number exceeding the critical value.

With a short axial length of an isolated rotor the flow of fluid throughthe rotor tends to be incompletely diffused by the expanding crosssectional areas of the rotor passages. Some fluid tends to pass throughWlitlOlli a significant reduction in velocity. This disadvantage isprecluded by giving a fluid a prewhirl before it reaches the rotor. Theprewhirl develops centrifugal pressure so that the fluid upon enteringthe radial diffusion rotorimmediately moves radially outward with theresult that the radial diffusion can be completed in a short rotorpassage. The rotor thus develops a greater pressure and a greaterefliciency. This prewhirl is developed in the stator blades.

Figs. 4 to 8 show a compressor incorporating the foregoing features.

In Fig. 4 the compressor is indicated generally by comprised of the case42 the rotors 41-46 and the stators 5l56. (See also Fig. 5.) Fluidenters the inlet and is pumped through the annular or main flow passage62 to the exit passage 64.

At the upstream end (Fig. 4) the stator 51 deflects the incoming air bymeans of the stator blades 66 in the direction of rotation 67 of rotor41 composed of blades 68. The next stator 52 also deflects the fluid inthe direction of rotation of rotor 42, but to a less extent, by blades70. At the third stage the stator 53 deflects the fluid substantiallyaxially toward the rotor 43. This stage is comprised of blades 74 and76.

In the succeeding stages of Fig. 4 the stator blades deflect the flowwith increasing peripheral velocity components against the direction ofmotion of the rotor blades.

The blades of the fourth stage are 78 and 80 and the blades of the fifthstage are 82 and 84. It s to be noted that in each of these statorstages (see Fig. 5) and in the sixth stator stage the stator blades arecurved to give the flow a progressively greater peripheral component insuccessive downstream stages.

The stator blades 86 for instance in the sixth stage have tail portionsdirected substantially in the peripheral direction.

In Fig. 7 the velocity vector 90 leaving the blade 86 when combined withthe peripheral velocity vector u of the rotor gives the velocity vector92 acting relative to the rotor 46. The vector 90 makes the positiveangle B with the axial direction and hence even for a great increase inaxial velocity through the compressor the direction of 92 relative tothe blades 94 of rotor 46 will change only a small amount in direction.

The rotor blades 94, Fig. 8, are hollow and as shown in Figs. 4 and 11each has its interior in communication by means of individual ducts 96with the hollow blades 76 of the third stage. Since the fluid pressureis greater in the sixth stage than in the third stage fluid will enterthe blades 94 through slot and be discharged through the discharge slots98 in blades 76. Thus the flow is induced to follow the curved portionof blade 94 making it possible to discharge the flow from the stage witha velocity direction perpendicular to the plane of rotation.

The last set of stators 100 (Fig. 4) takes out the peripheral componentof velocity relative to the case 42 and directs the discharge of fluidaxially along the passage 64.

As an alternate form the rotor may be formed as in Fig. 9. Here theblade is made in two parts, the fore part 102 and the aft part 104spaced from the fore part to provide the slot 106. The flow through theslot provides a jet to control the boundary layer on the convex portionof the blade and induce the flow in the passage 108 between blades 102to follow the blade surface.

The stators as shown in Fig. 4 are also inter-connected by ducts such as109 to provide for flows of fluid through the blade slots. Thisconstruction is similar to that shown in my U. S. Patent No. 2,344,835issued March 21, 1944.

By providing the stator which gives a large positive angle B, thevariation 6 (Fig. 3) is kept small and consequently the blades 94 (Figs.4 and 5) may be thin at the nose and particularly efficient for highvelocities of flow.

As shown in Figs. 4 and 10, particularly the latter, the case 42diverges from the wall 110 of the rotor 48 so that each passage 112between blades 94 is expanding in cross sectional area until thelocality of the blade curvature is reached where the passage area ispreferably made to contract slightly so that the flow about the curve isin a favorable pressure gradient. This facilitates an eflicient flowabout the curve.

There is also another advantage in the divergence of the hub and casewalls. The increase in the cross sectional areas of the rotor passagesin the downstream direction slows down the velocity of flow before theflow is turned by the blade. Hence the appearance of compressibilityshock waves is delayed. That is, the peripheral tip speed of the bladescan be higher before the shock wave appears in the passages betweenblades. This means that substantially greater pressure ratios can beobtained from a rotor.

The first shock waves appear at the leading edge of a. blade but thecritical shock wave which limits the mass flow through the rotor occursin the passage downstream from the nose of the blade.

If the passages between blades begin to diverge radially opposite theblade noses the radial expansion can compensate for the peripheralcontraction due to the blade thickness. Hence there need not be a throatalong the passages between blades or at least the throat may be placedfar downstream from the inlet of each rotor passage. In this connectionthe blades may have substantially parallel sides as shown by blades 102in Fig. 9.

The opposite sides of the blade sections such as blades 86 (Fig. 5) aresubstantially parallel along a substantial length between the noseportion and the aft portion.

By making the last stage with thin blades and relatively sharp noses itcan operate with very high fluid velocities without generating shockwaves at the nose or in the passage. However in some applications thevelocity may become supersonic in the last stage if the back pressure isreduced sufliciently when the rate of rotation of the rotor is near theoptimum speed for the compressor as a whole. For this reason the type ofrotor shown in the last stage is very advantageous since it can operateeven at a supersonic velocity as has been disclosed in my applicationSerial No. 624,013 filed October 23, 1945, now Patent No. 2,648,493,entitled Compressors. Furthermore for a high performance compressor thelast stage is preferably made to have a supersonic velocity of approachof the air at the optimum condition of operation. For such a compressorit is important that the angular range of the approach vector should besmall to obtain the proper shock waves at the nose of the blades andwithin the rotor or stator passages. These are provided by thisinvention.

In an axial flow compressor if the pressure rise is great between inletand exit for the design condition, then the machine will be much lesseflicient at a lower delivery, that is at a lower value of the mass offluid delivered per revolution. The greater the pressure rise, thegreater the drop in etficiency at an off-design delivery.

The compressor of this invention using the type of rotor 48 is providedto assuage this undesirable condition and places the axial flowcompressor on a more favorable footing with respect to othercompressors, such as for instance the centrifugal compressor, thanheretofore existed.

When the fluid approaches the blades at supersonic values shock wavesfirst appear at the leading edges of the blades and if the back pressureis substantial the shock waves may occur ahead of the leading edges andthe flow may refuse to enter the passages between the blades at highsupersonic velocities. This difliculty can be overcome by dischargeslots properly located with respect to the leading edges of the blades.

Figure 12 shows an alternate structure for the last rotor and the statorahead of it. The balance of the compressor ahead of this stator wouldhave a structure simi lar to that of Figs. 4 and 5.

In Fig. 12 the slots 140 and 142 are located in peripheral walls, thatis the shroud ring 143 and the hub wall respectively. That is the rotorblades 144 of the last rotor are encircled by the shroud ring and itsleading edge forms the slot 140 with the case wall 42'.

Air for the case or outer wall slot 140 is bled from the passage 64 viathe annular duct 150 formed in the case. The air is at a higher pressurein 64 than in the passage at the leading edge of blade 144 and hence canflow at a higher velocity from the slot 140 than the velocity of thelocal main flow.

Air is also supplied from duct 150 to the slot 152 positioned in therotor passage 62 a substantial distance inward from the leading edge ofblade 144.

Air is also supplied to the slot 142 and slot 156 from passage 64 viathe annular ducts 160 and 162. Air also enters the hollow interior ofblade 144 via 162 to serve the slot 164.

The discharge slots 170 and 172 of stator blade 174 are also served withair from duct 150. As shown in Fig. 13 this blade has a well roundednose 176 and the discharge slots located near the ends of the nosecontour.

The passages 112 in the rotor between the blades in Fig. 12 are similarto those in Fig. 8 and are bounded by walls on four sides. The walls 110of the hub of the rotor and the shroud ring 143 bound the passage onradially opposite sides while the adjacent blades bound the other twoopposite sides. All of the walls may have slots therein but preferablyonly hub and case walls and one blade have slots. The slots in oppositewalls within the passages are preferably not directly opposite eachother.

The blades discussed herein are to be considered thin blades if theirmaximum thickness is less than 15 per cent of the blade section chordlength.

In the preferred forms of the blades the chordwise length of the blade,that is the dimension along the direction of flow is preferably smallerthan the spanwise dimension or length or at least the chord is not morethat twice the span. The blades also have free leading and trailingedges extending in the same general radial direction.

Axial flow compressors have blade structures whose flow passages betweenblades extend in the general axial direction from an inlet at the frontto an exit at the rear to discharge fluid in the general axialdirection.

It will now be clear that I have provided a compressor which can operateefficiently over a wide range of mass flow rate per revolution. This isaccomplished by thickening the noses of the blades in successive stagesto take advantage of the increasing value of the velocity of sound inthe compressed fluid; also by arranging the blades so that there is onlya small range of approach angles for the blade to handle. This is veryimportant for a supersonic rotor. It is also particularly advantageousin the last stage where it is desirable to add a large pressure increaseand at the same time reduce the axial velocity. This is accomplished bythe special rotor of the last stage which has expanding cross sectionalareas of the passages between blades.

There are many applications, in aircraft particularly,

where a short compressor is significant. For instance the velocity offlow through a combustion chamber of a gas turbine should be low but thedischarge velocity of a compressor is high. Consequently the combustionchamber must be connected to the compressor by an expanding tube toreduce the velocity. The special rotor of this invention expands theflow and lowers the velocity in one stage of the compressor whilecompressing, thus doing away with the need of a long diffuser.

While I have illustrated a specific form of this invention it is to beunderstood that I do not intend to limit myself to this exact form butintend to claim my invention broadly as indicated by the appendedclaims.

I claim:

1. In combination in a compressor adapted to have a flow of fluid ofsupersonic velocity relative to compressor blades thereof, a walldefining a case, a hub including a hub peripheral wall mounted in saidcase for rotation about an axis, a plurality of axial flow bladesmounted on said hub wall and spaced peripherally therea'oout to define aplurality of rotor passages, each said blade having a fore portiondirected at a substantial angle to said axis of rotation and toward thedirection of said rotation, said blades having their aft portions curvedto be more nearly parallel to said axis than to the said direction ofsaid fore portion, each said blade having a tapered blade section withits maximum thickness positioned between its leading and trail ing endsgiving to each said rotor passage :1 reduced peripheral width positionedbetween blade leading and trailing edges, said case and hub wallsbounding said passages on the peripheral sides thereof, said case andhub walls departing from each other along said axis in the downstreamdirection at a rate to exclude reduced cross sectional areas betweensaid leading edges and the position of said maximum thickness, the crosssectional areas of said passages defined by said walls and said aftportions of said blades decreasing rearward therealong, theconfiguration of said rotor passages adapting said rotor for rotation atsupersonic velocity relative to said case for the efiicient compressionof said fluid.

2. In combination in a compressor adapted to have a flow of fluid ofsupersonic velocity relative to the compressor blades, a wall defining acase, a rotor including a hub peripheral wall mounted in said case forrotation about an axis and a plurality of axial flow blades mounted onsaid hub wall and spaced peripherally thereabout to define a pluralityof rotor passages, and a stator comprised of a plurality of statorblades supported in said case upstream adjacent to said rotor, saidstator blades being spaced peripherally to define therebetween aplurality of stator passages whose exits have decreased cross sectionalareas relative to their inlets, said stator blades being set at apositive angle relative to the direction of said axis to direct thefluid flow against the direction of rotation of said rotor, each saidrotor blade having a tapered blade section with its maximum thicknessbetween its leading and trailing ends giving to each said rotor passagea reduced peripheral width positioned between said blade leading andtrailing edges, said case and hub walls bounding said rotor passages onthe peripheral sides thereof, said case and hub walls departing fromeach other along said axis in the downstream direction at a rate toincrease the cross sectional areas between said leading edges and theposition or said maximum thickness, said rotor passages adapting saidrotor for rotation at said supersonic velocity for the eificientcompression of said fluid, said rotor blades being set at a substantialangle relative to the direction of said axis with said leading edgestoward the direction of rotation to adapt said rotor for supersonicoperation in cooperation with said stator passages of said decreasedexit cross sectional area.

3. In combination in a compressor, a wall defining a case, a hubincluding a hub peripheral wall mounted in said case for rotation aboutan axis, said walls defining an annular passage for a main flow of fluidtherethrough, a plurality of axial flow blades mounted on said hub walland spaced peripherally thereabout to subdivide said annular passageinto a plurality of rotor passages, each said blade having a taperedblade section with its maximum thickness positioned between its leadingand trailing edges giving to each said passage a portion of reducedperipheral width whereby the sum of said widths is less than theperipheral width of said main passage upstream adjacent to said leadingedges, said case and hub walls bounding said rotor passages on theperipheral sides thereof, said case and hub walls departing from eachother along said'axis in the downstream direction at a rate to exclude areduced cross sectional area for each said passage aft of said leadingedge for a substantial distance rearward therefrom to reduce shock wavelosses adjacent said leading edges.

4. In combination in an axial flow compressor adapted to have a flow offluid therethrough, a case, a rotor having a hub and a plurality ofperipherally spaced blades mounted thereon with rotor flow passagestherebetween, each of said blades having a locality of maximum thicknessbetween the leading and trailing edges thereof, means mounting saidrotor in said case for rotation about an axis, said rotor blades eachhaving a substantially straight fore portion and a curved aft portion,said case and hub having wall portions at the radially outer and innerperipheries of said rotor blades respectively bounding said passages onthe peripheral sides thereof, said wall portions along said straightfore portions of said blades diverging one relative to the other in thedownstream direction, one of said wall portions along said curved aftportions of said blades converging relative to the other said wallportion to deflect said flow efiiciently.

5. In combination in a compressor adapted to have a flow of fluidtherethrough, peripheral walls spaced apart radially defining an annularduct having a longitudinal axis, a plurality of radially extendingblades in said duct spaced peripherally to define a plurality of axialflow passages therebetween, each said blade having a substantiallystraight fore portion and a curved aft portion, the portions of saidwalls at the radially inner and outer ends of said blades diverging onerelative to the other along said fore portions of said blades andconverging along said said aft portions thereof to vary the crosssectional areas of said passages to deflect said flow efficiently.

or In combination in an axial flow compressor adapted to have a flow offluid therethrough, a case, a rotor comdivering rearward along the axialdirection to give said fore portions" of said passages increasing radialwidth and cross sectional areas rearward therealong, the cross sectionalareas of the portions of said passages defined by the aft portions ofsaid blades and said walls decreasing rearward therealong, the foreparts of said blades being set at a substantial angle relative to thedirection of said axis to subject said passage inlets to the relativeperipheral velocity of the fluid.

7. In combination in a compressor, a case, a rotor having a hub andblades mounted thereon, means mounting said rotor in said case forrotation about an axis, said rotor blades having a substantiallystraight fore portion of substantial chordwise length succeeded by acurved aft portion of substantial chordwise length, said case and hubdefining peripheral walls diverging rearward in the axial directionalong said straight fore portions and converging along said curved aftportions of said blades, said case fitting closely to said blades at thetips thereof along the chordwise length thereof, said case, rotor, andblades having walls defining a plurality of rotor flow passages, atleast someof said walls in the vicinity of said curved aft portions ofsaid blades having slots therein, and duct means adapted to have a flowof fluid therein in communication with said slots to induce flows offluid through said slots.

8; In combination in a compressor adapted to have a flow of fluidtherethrough of supersonic velocity relative to compressor bladesthereof, a wall defining a case, a rotor having a hub peripheral walland blades mounted thereon, said blades being spaced peripherally todefine a plurality of rotor flow passages therebetween, means mountingsaid rotor in said case for rotation about an axis, said blades beingset at a substantial angle relative to the direction of said axis withtheir leading edges toward the direction of rotation, each said rotorblade having a fore portion and a curved aft portion, said walls ofsaidhub and case diverging one relative to the other along said foreportions of said blades providing cross sectional areas of said passagesincreasing in the downstream direction to reduce the flow velocitybefore the flow reaches said curved aft portion, said hub and case wallsconverging one relative tothe other along said aft portions of saidblades, the outer ends of said blades being shaped to fit closelyagainst said case wall along the chordwise length of each blade.

References Cited in the tile of this patent UNITED STATES PATENTS1,447,554 Jones Mar. 6, 1923 2,084,462 Stalker June 22, 1937 2,314,058Stalker Mar. 16, 1943 2,314,572 Chitz Mar, 23, 1943 2,410,769 BaumannNov. 5, 1946 2,505,755 DeGa'nahl May 2, 1950 2,527,971 Stalker Oct. 31,1950 FOREIGN PATENTS 504,214 Great Britain Apr. 21, 1939

